import * as Cesium from "cesium";

export default class SnowEffect {
  constructor() {
    this.stage = null;
  }

  init(viewer) {
    this.stage = new Cesium.PostProcessStage({
      name: 'czm_snow',
      fragmentShader: `
        uniform sampler2D colorTexture;
        uniform float snowSpeed;
        uniform float snowSize;
        in vec2 v_textureCoordinates;
        out vec4 fragColor;

        float snow(vec2 uv,float scale) {
          float time=czm_frameNumber/snowSpeed;
          float w=smoothstep(1.,0.,-uv.y*(scale/10.));if(w<.1)return 0.;
          uv+=time/scale;uv.y+=time*2./scale;uv.x+=sin(uv.y+time*.5)/scale;
          uv*=scale;vec2 s=floor(uv),f=fract(uv),p;float k=3.,d;
          p=.5+.35*sin(11.*fract(sin((s+p+scale)*mat2(7,3,6,5))*5.))-f;d=length(p);k=min(d,k);
          k=smoothstep(0.,k,sin(f.x+f.y)*snowSize);
          return k*w;
        }

        void main(void){
          vec2 resolution=czm_viewport.zw;
          vec2 uv=(gl_FragCoord.xy*2.-resolution.xy)/min(resolution.x,resolution.y);
          vec3 finalColor=vec3(0);
          float c=0.;
          c+=snow(uv,30.)*.0;
          c+=snow(uv,20.)*.0;
          c+=snow(uv,15.)*.0;
          c+=snow(uv,10.);
          c+=snow(uv,8.);
          c+=snow(uv,6.);
          c+=snow(uv,5.);
          finalColor=(vec3(c));
          fragColor=mix(texture(colorTexture,v_textureCoordinates),vec4(finalColor,1),.5);
        }
      `,
      uniforms: {
        snowSpeed: 60.0,
        snowSize: 0.02
      }
    });
    viewer.scene.postProcessStages.add(this.stage); // 添加雪景效果
  }

  show(visible) {
    if(this.stage) this.stage.enabled = visible; // 显示或隐藏雪景效果
  }


}
